The present invention relates to a semiconductor device and a manufacturing method therefor.
As a semiconductor device used for reading DVD (Digital Versatile Disc) and the same, there has been known a device, as shown in FIG. 13, composed of a silicon submount photodiode chip 111, and a red color laser diode 13 serving as a laser chip die-bonded onto the silicon submount photodiode chip 111.
The silicon submount photodiode chip 111 includes an N+-type silicon substrate 1, an N−-type silicon epitaxial layer 2 on the N+-type silicon substrate 1, a P-type diffused layer 3 as a receiver formed in the N−-type silicon epitaxial layer 2, an insulating film 104 covering the surfaces of the N−-type silicon epitaxial layer 2 and the P-type diffused layer 3, and an electrode 112 formed on the insulating film 104. The electrode 112 is made up of an Al layer 105, a TiW/Au layer 106, and an AuSn layer 107. The Al layer 105 is in ohmic contact with the P-type diffused layer 3 and an N-type diffused layer (unshown). A TiW layer in the TiW/Au layer 106 functions as a barrier metal, while an Au layer in the TiW/Au layer 106 improves adherence between the TiW layer and the AuSn layer 107. The AuSn layer 107 functions as a solder to adhere to an unshown Au electrode of the red color laser diode 13. The red color laser diode 13 is composed of a P-type layer 8 with a thickness of 5 to 6 μm, and an N-type layer 9 with a thickness of approx. 110 μm, to radiate a laser beam of 654 nm.
For manufacturing the above background art semiconductor device, the red color laser diode 13 is mounted on the electrode 112, and heat of 380 to 400° C. is applied for 12 minutes to weld the AuSn layer 107 and the Au electrode (unshown) of the red color laser diode 13. The red color laser diode 13 is susceptible to heat. Accordingly, if the red color laser diode 13 is used for a long period of time under high temperature conditions, an operating current necessary for obtaining a desired optical output is gradually increased by deterioration of elements. As a result, the red color laser diode 13 gets thermal destruction due to thermorunaway. To prevent such thermal destruction, thickness of the P-type layer 8 is reduced for decreasing thermal resistance.
FIG. 14 is a plane view showing the above-stated background art semiconductor device from the upper side. It is noted that the red color laser diode 13 is depicted with an alternate long and two short dashes line in FIG. 14.
In the above-structured semiconductor device shown in FIG. 14, the red color laser diode 13 is mounted on the AuSn layer 107. A light beam radiated from the back side of the red color laser diode 13 is received by the P-type diffused layer 3, by which an output of a light beam radiated from the front side of the red color laser diode 13 is monitored. In other words, based on the light beam radiated from the back side of the red color laser diode 13, the optical output from the front side of the red color laser diode 13 is monitored.
In an equivalent circuit of the semiconductor device shown in FIG. 15, a photodiode 1110 corresponding to the silicon submount photodiode chip 111 is connected to the red color laser diode 13 through a common cathode.
However, since the red color laser diode 13 is different in band-gap structure from an infrared laser diode, using the background art semiconductor device at ambient temperature of 80° C. or higher decreases efficiency of the optical output under high temperature conditions. As a result, an operating current of the red color laser diode 13 is increased, and continuous application of voltage to the red color laser diode 13 in such a condition may result in thermal destruction.